Bubble traps are used in a variety of technical fields as components in hydraulic circuits where the presence of bubbles of gas is undesirable. By way of example, the hydraulic circuit of apparatus used in renal dialysis for fabricating a dialysis liquid and causing it to flow through a membrane exchanger includes several bubble traps, without which the transfer rate in the exchanger would be reduced, the operation of the pumps would be disturbed, and measurements of the quantity of blood plasma ultrafiltering through the membrane, if any, would be erroneous.
In conventional manner, a bubble trap used in that type of apparatus comprises a slightly tapering vessel closed by a cover having a bulge, with a closable purge duct being connected to the top thereof. The vessel is divided into two over a portion of its height by means of a transverse partition, with liquid being let in and let out on respective opposite sides of the partition. The function of the partition is to prevent liquid that enters the bubble trap escaping therefrom immediately. The top of the bubble trap is provided with a liquid detector which is used to cause the purge duct to be opened each time that the detector no longer detects the presence of liquid. By way of example, a bubble trap of this type having an internal volume of about 150 ml can be used to extract about 4.5 ml of air (measured at atmospheric pressure) per minute from a liquid flowing at a rate of about 1200 ml/min.
The conventional bubble trap described above suffers from several drawbacks. Given its shape, the volume of air removed on each purge is relatively large, thereby disturbing the flow of the liquid, in particular at the inlet and at the outlet of the bubble trap. In addition, compared with the volume of the tubular ducting of the circuit, the volume of the bubble trap is not negligible, which means that putting the apparatus into operation (sterilization, initial filling, warming up) takes quite a long time. Finally, the bubble trap can never be completely emptied.
Patent document U.S. Pat. No. 4,493,705 describes a blood container constituted by a banana-shaped flexible bag having an inlet and an outlet that extend the central axis of the bag, and also having a vent situated at the top of the bag approximately halfway between the inlet and the outlet. Although the shape of that container causes the fluid flowing therethrough to slow down in its middle portion, it is not designed to cause eddies to disappear nor to enhance the removal of bubbles from the flowing liquid. In addition, that container requires manual intervention to empty it.
An object of the present invention is to provide a bubble trap that gives optimum performance while being of small volume and being capable of being emptied completely.